Long-term impact of prescribed fire on soil chemical properties in a wildland-urban interface. Northeastern Iberian Peninsula

Abstract

Wildfires are common in wildland-urban interfaces (WUIs), where they represent a severe threat to inhabited urban settlements endangering both infrastructure and human life. Given these hazards, it is critical that forest management tools be designed to reduce the risk of wildfire at the WUI. In this regard, a management tool that is increasingly being adopted is that of prescribed fires; however, a complete understanding of their impact has yet to be gained. The aim of this study, therefore, is to analyze long-term soil properties after a prescribed fire and observed if the prescribed fire avoids vegetal fuel continuity. Our study area occupies a Mediterranean forest in the urban settlement of Picarany in the municipality of Almoster (Tarragona, Spain). The vegetation is composed primarily of Pinus halepensis Miller. and Quercus ilex L. and the soil type is classified as Xerorthents. Soil sampling was carried out in four campaigns: just before the prescribed fire (BPF), just after (APF), one year after (1YAPF) and 13 years after the prescribed fire (13YAPF). In each sampling period, 30 samples were taken (0-2.5 cm) from a 72-m² experimental plot (4 × 18 m). The soil properties analyzed were total nitrogen (TN), soil organic matter (SOM), pH, electrical conductivity (EC) and extractable calcium (Ca), magnesium (Mg), potassium (K) and available phosphorus (P) concentrations. The carbon/nitrogen ratio was also calculated. A comparison of pre-fire values (2004) with long-term results (2017) shows increases of EC, Ca and Mg and decreases of TN and SOM. Despite these changes, the prescribed fire was found to be a good tool for managing forest areas. Indeed, the changes in soil properties did not represent a severely degradation of the soil and after 13 years there was no horizontal or vertical fuel continuity in the wildland-urban interface.

Keywords: Long-term post-fire; Soil chemical properties; Wildfire risk; Wildland-urban interface.